[6.7RC] Whole RC got slow disk performance issue

This is to report whole 6.7RC got slow disk performance, I have setup as below

- 3 disk connect to LSI HBA

- 1 SSD connect to onboard SATA

- each disks have only one 24GB file for testing

- same issue reproduce on 3 different PC platform

Test by cat /mnt/disk(x)/xxxx > /dev/null

In 6.6.7, even 3 disk read at same time, throughput was normal

But after 6.7RC, even onlyone disk access, throughput already drop.

I also make test on SSD which connect to onboard SATA to eliminate the issue cause by HBA.